The standard production process for producing helically corrugated metal pipe is well known and involves first forming lengthwise corrugations in an elongated strip of sheet metal, with the corrugations extending along the length of the strip. The corrugated strip is then spiraled into a helical form so that opposite edges of the corrugated strip come together and can be either crimped (commonly referred to as lock seaming) or welded to form a helical lock along the pipe.
U.S. Pat. No. 4,791,800 to Alexander describes a roll forming process for making box-shaped ribs in a sheet material, such as steel, utilizing a series of tooling stands through which the sheet material is moved. The system of U.S. Pat. No. 4,791,800 typically includes additional tooling stands to further flatten the curved areas of the strip (shown in FIG. 4 of U.S. Pat. No. 4,791,800) and to form edges for lock seaming.